1. Field of the Invention
The present invention relates to an image sensing device and image sensing system.
2. Description of the Related Art
In a CMOS sensor which is an image sensing device using a MOS transistor, multiple pixels are arranged two-dimensionally as disclosed in Japanese Patent Laid-Open No. 09-046596. In each pixel, as illustrated in FIG. 2 of Japanese Patent Laid-Open No. 09-046596, charges generated through photoelectric conversion by a photoelectric conversion unit 1 of a photodiode are transferred to a floating fusion unit (FD unit) 21 and consequently potential of the FD unit 21 changes. Each pixel amplifies a change in the potential of the FD unit 21 using a source-follower amplifier MOS transistor 5 and outputs the change as a signal to a vertical output line.
Japanese Patent Laid-Open No. 2005-167958 describes how the number of lines per photoelectric conversion cell (91 or 92) can be reduced when four PD units 2, 3, 6, and 7 share one FD unit 10 and one pixel amplifier MOS transistor 24 as shown in FIG. 1 of Japanese Patent Laid-Open No. 2005-167958.
Incidentally, the present inventor has found out the following new problem. What is at issue in reducing the pixels of a CMOS sensor is diffraction of light by wiring which defines an aperture region of a photodiode.
Specifically, the wiring which defines the aperture region of the photodiode is located above the photodiode, for example, via a transparent interlayer insulating film with a thickness on the order of a few hundred nm to a few μm. In this case, when pixel pitch is 2 μm or less and width of the aperture region is less than 2 to 3 times the incident wavelength, part of light incident upon a given pixel reaches the photodiode of an adjacent pixel after being diffracted by the wiring which defines the aperture region. This causes optical mixture of colors.